EXHIBIT 5.1 January 21, 1994 Securities and Exchange Commission Judiciary Plaza 450 Fifth Street, N.W. Washington, D.C. 20549 Re: KLA Instruments Corporation Registration Statement on Form S-3 Ladies and Gentlemen: As counsel to KLA Instruments Corporation, a Delaware corporation (the "Company"), we are rendering this opinion in connection with a proposed sale by the Company of up to 2,300,000 shares of its common stock, $.001 par value ("Common Stock"). We have examined all instruments, documents, and records which we deemed relevant and necessary for the basis of our opinion hereinafter expressed. In such examination, we have assumed the genuineness of all signatures and the authenticity of all documents submitted to us as originals and the conformity to the originals of all documents submitted to us as copies. Based on such examination, we are of the opinion that the 2,300,000 shares of Common Stock to be issued and sold by the Company (of which up to 300,000 shares are to be issued to cover over-allotments, if any) are duly authorized shares of Common Stock and, when issued against payment of the purchase price therefor, will be validly issued, fully paid and nonassessable. We hereby consent to the filing of this opinion as an exhibit to the above-referenced Registration Statement and to the use of our name wherever it appears in said Registration Statement, including the Prospectus constituting a part thereof, as originally filed or as subsequently amended. Respectfully submitted, GRAY CARY WARE & FREIDENRICH A Professional Corporation